The present invention relates to a soft and elastic prosthetic sleeve, and more exactly to a liner blank provided for customizing through thermoplastic deformation and adaptation to the individual wearer of a prosthetic device.
In connection with amputation of an extremity, i.e. a leg or an arm, an amputation stump or residuum often remains to serve for attachment of a prosthetic device. The amputation stump is inserted into a rigid sleeve or socket that forms an attachment for the prosthetic device, which for example may be a foot or a lower leg with foot in case the stump is situated below the knee of a leg. Similarly, the prosthesis may be an entire prosthetic leg, whereby a remaining portion of the thighbone is fitted into a corresponding prosthetic socket. A lower arm or upper arm prosthesis may be attached in a corresponding way to a hand or arm prosthetic device.
The socket often has a generally conical shape, one end of which is open and the other being completely closed and having a somewhat rounded off shape. Additionally, the socket may be adapted to the shape of the amputation stump. Prosthetic devices consequently confines what is left of the extremity in a specially adapted socket attached to the prosthesis, the socket transferring forces between the prosthesis and the remaining portion of the extremity.
An individually adapted socket is manufactured by producing a copy of what is left of the extremity. Today there are mainly two methods utilized to do this, either a laser scanner is used which is imaging the body portion to be copied, then the values read by the scanner are transferred to a milling cutter that mills a copy of the body portion, or a negative plaster cast is made by means of plaster bandage, where after the negative plaster cast is filled to create a positive copy of the body portion. Then by means of the positive copy a rigid prosthetic socket is molded for a close fit about the amputation stump. A disadvantage with such copies is that they are true copies only at the time of the plaster casting. The reason for this is that the human body is continuously changing and especially then the portion left of an amputated extremity, the atrophy being large (in time it decreases in volume).
The problem of the rigid socket is that it does not follow the changes in volume, and the remains of the extremity is soft and sensitive while the socket member is hard, which may result in the extremity being chafed if there is not a softer sleeve or liner inside the socket. Therefore today different kinds of prosthetic socks or soft sleeves/liners are used inside the rigid outer sleeves/sockets.
U.S. Pat. No. 5,376,132 (Caspers) suggests a prosthetic liner and socket that is adapted to the shape of the residuum. A viscous fluid mixture of polymer components is introduced to set and cure in a spacing that is formed between a reduced positive model of the residuum, and an outer, negative mold. This method of forming the liner with socket in adaptation to the shape of the residuum is complex and involves a plurality of method steps a to k for molding the liner to the shape of the individual wearer.
U.S. Pat. No. 5,603,122 (Kania) suggests a form fitting sleeve member with a contoured form fit. A stretchable, elastic textile fabric is used for producing a form fit sock by sewing together two or three pieces of the material, cut into suitable patterns for a certain degree of adaptation to the shape of an amputation stump. The sock member is impregnated with polymeric material that provides a cushioning interface between the residuum and a rigid prosthetic socket.
Another prior art soft liner is one made of silicone and disclosed in SE 454 943 B. A drawback of this sleeve is that it is not able to be particularly adapted to the amputation stump. On the contrary, the sleeve is so elastic that it can encircle the amputation stump, but as no amputation stump in reality is shaped conically, there will be higher pressure and stress applied to the following portions of the amputation stump:                in areas where the diameter of the stump is larger than the silicone sleeve, which means that the surface pressure on the stump will be relatively higher in these areas compared to other areas;        in areas, where the stump has a small radius, e.g. a prominence due to underlying bone, which means that the surface pressure over the prominence locally increases when the elastic sleeve is tightened over the prominence.        
See also example of FIG. 4, which illustrates a soft elastic sleeve rolled onto a stump of a lower leg amputee, illustrating how the distal tibia point creates a bone prominence on the left hand side of FIG. 4.
Not only the pressure at the exposed portions will increase, but with stretching of the sleeve in these more sensitive areas, a larger loss of entropy arises in the sleeve at these areas, in other words the molecule chains are stretched, which in turn decreases their mobility and the soft sleeve becomes harder in the sensitive areas.
Elastic materials harden when they are stretched, and an uneven stress will be encountered when the most expanded portions of the elastic sleeve are placed over the prominences, which results in discomfort and the user being chafed.
Most of the users of prosthetic devices are lower leg amputees and elderly persons, and therefore do sit for longer times also when wearing a prosthetic device. One problem of common soft sleeves is that they fold at the back of the knee when the knee is bent, which results in discomfort chafing and, in the worst case, that the flow of blood is obstructed and a so called stasis condition arises. Note in FIG. 4 how the sleeve is folded at its upper right portion.
Accordingly there is a need for a soft elastic liner that avoids the drawbacks discussed above and which provides a comfortable support of a prosthetic device.